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When can plant populations be invaded by other species?

The world is experiencing increasing climatic variability, loss of biodiversity, and spread of invasive species. Together, these factors can have huge effects on the functioning of our ecosystems. But what makes ecological systems more resistant to biological invasions? And how do different processes of environmental change interact?

Previous research has shown that genetically more diverse systems are better at preventing invasion of exotic species and that environmental fluctuations, in contrast, can promote invasions. In our study, we were particularly interested in the combined effect of these two factors – which has never been tested before.

We sowed experimental populations of the annual plant Arabidopsis thaliana containing 1, 3 or 6 different genotypes (randomly chosen out of 8) and added seeds of another annual plant, Senecio vulgaris, as an invader. We then subjected these communities to either constant or weekly fluctuating temperatures, such that the overall mean temperature stayed the same over the course of the experiment. After several weeks we harvested the communities and assessed various performance traits of Arabidopsis and Senecio.

We found that monocultures of the eight Arabidopsis genotypes varied in their biomass, and that more successful Arabidopsis genotypes had a stronger negative impact on the success of Senecio, demonstrating that within-species genetic variation can have important ecological effects. In line with previous studies, the invasion resistance of experimental plant populations – measured as the biomass ratio between Arabidopsis and Senecio – tended to increase with increasing genotypic diversity. Against our expectation, temperature fluctuations strongly favoured Arabidopsis over Senecio, which may be particular to the choice of species in our study. We found no interactions between genotypic diversity and temperature fluctuations. However, the different temperature regimes caused shifts in the magnitude of net diversity effects and transgressive overyielding (i.e. different mechanisms how diversity effects can be expressed), suggesting that increasing temperature variability could influence invasion resistance.

Concluding, our study demonstrates that genotypic diversity and temperature variability independently affect the invasibility of plant populations. Our results strengthen the notions that maintaining genetic diversity of populations can help to resist invasions, and that environmental fluctuations can alter invasion success.

Oikos Journal

Oikos is a journal issued by the Nordic Ecological Society and is one of the leading peer-reviewed journals in ecology. Oikos publishes original and innovative research on all aspects of ecology, defined as organism-environment interactions.